Windshield displays that use the entire windshield as a display are being developed for vehicles such as automobiles. Several technologies are suitable to provide windshield displays including, but not limited to: electrowetting cells, organic light emitting diode (OLED), liquid crystal device (LCD), and projection type displays using lasers or other light projection devices. Government regulations generally specify a degree of transparency for vehicle windshields. However, regulations pertaining to windshield displays have yet to be developed. What is needed is a way to determine that a vehicle operator's field of view to an area in front of or around the vehicle is not being obstructed by a windshield displays installed in the vehicle.